A flat panel display such as an liquid crystal (LC) pixel matrix display or an organic light emitting diode (OLED) pixel matrix display can function as a dual view display, in which in a horizontal direction a first view can be generated along a first viewing angle range and a second view can be generated along a second viewing angle range. Such a dual view display is capable of generating two different views at the same time by assigning one half of the pixels of the pixel matrix to the first view and another half of the pixels of the pixel matrix to the second view.
A well known method to obtain two views from a single pixel matrix display is the application of a single straight barrier, which incorporates vertical openings in an otherwise opaque barrier layer. The vertical openings extend substantially continuous along the vertical length of the pixel matrix. However, such a solution to obtain Dual view from a single pixel matrix is adversely affected by a relatively poor horizontal resolution. To solve the poor resolution so-called stepped barriers are applied. A particular application is the so-called double stepped barrier arrangement (double barrier). Such a double barrier comprises a first barrier layer below and a second barrier layer above the pixel matrix. The barrier layers comprise two-dimensional patterns that allow that the first and second views to be generated by the pixel matrix while using a single light source. However, it has been found that the use of two barrier layers adversely affects the construction of the dual view display since a variation of the thickness of the glass substrates carrying the barrier layers and the pixel matrix display can affect the quality of a produced image.
Dual view displays are used, for example, in automotive applications as displays that can be used simultaneously by a driver and a passenger. The driver will see the first view, which for example shows a display that relates to parameters of the automobile such as a route navigation display. The passenger may see a second view, for example a TV broadcast or a video.
For reasons of safety, the driver should not see the second view while driving. Therefore, cross-talk of the first view and the second view, i.e., a (partial) perception of the second view (for the passenger) within the viewing angle of the first view (for the driver), should be avoided.
It is recognized that cross-talk between first and second views may occur not only in the horizontal direction but also the vertical direction. In particular, at relatively large oblique angles in the vertical direction an undesired second view may be visible to the driver either directly or through a reflection of the undesired second view in a front windscreen of the automobile. In displays from the prior art, an undesired viewing in the vertical direction is suppressed by a Louvre film (or Light Control film (LCF)) to avoid reflection in the windscreen. Such a Louvre film is relatively expensive. Moreover, the Louvre film reduces a brightness of the display by about 30%.
FIG. 1 depicts a horizontal cross-section of a dual view display D1 using a double barrier. The dual view display D1 of the prior art shown here, using a double stepped barrier, is an LCD type display. The display comprises a color filter plate CF, a first barrier layer LR1, a second barrier layer LR2 and a backlight BL. The cross-section shown here is taken along a horizontal direction X of the display. For ease of explanation, the polarizers and liquid crystal elements are not indicated here.
The first barrier layer LR1 is arranged in a height direction Z between the backlight BL and a side of the color filter plate CF facing the backlight. The first barrier layer LR1 comprises a transparent carrier plate (such as a glass plate) on which blocking elements BS are arranged. The blocking elements BS are separated from each other by openings WO.
Above the color filter plate CF (along direction Z), i.e., at a side of the color filter plate not facing the backlight, the second barrier layer LR2 is arranged. The color filter plate CF comprises a transparent carrier plate on which a sequence of transparent color elements are arranged. The color elements comprise red elements R, green elements G and blue elements B, that are configured to generate light of a red color (R), green color (G) or blue (B) color, respectively, when, during use, light from the backlight BL passes through the respective color element. Next to the color filter plate CF, an array plate (not shown) is arranged, comprising array metals M2 (i.e., metallic connection line M2 and/or metallic light shield).
The opaque metallic connection line M2 and/or metallic light shield M2 are positioned in such a way that the color elements R, G, B appear to be separated from each other by a non-transparent interface area, which corresponds to the metallic connection line M2 and/or metallic light shield M2. For reasons of clarity, the array plate and color filter plate are shown here in a composition, and not as individual items. Below, the composition of the array plate and color filter plate will be referred to as the color filter plate, unless indicated otherwise. The metallic connection line and/or metallic light shield will be explained in more detail below.
The color elements R, G, B extend in columns along a vertical direction Y. The color elements R, G, B relate to sub-pixel elements, which in a combination comprise at least a red, a green and a blue element, are paired as a pixel element of the display. The R-G-B color elements are dedicated to either the first view or the second view. In FIG. 1, color elements indicated by R1, G1, B1 are dedicated to the first view, while color elements indicated by R2, G2, B2 are dedicated to the second view. Note that due to the geometry of the barriers and the required views, pixels are paired in an interleaved order. In FIG. 1, red color element R1 for the first view is adjacent to green element G2 for the second view. Green element G2 is next to blue element B1 for the first view. The blue element B1 is next to red element R2 for the second view V2. The red color element R2 for the second view is adjacent to green element G1 for the first view. Green element G1 is next to blue element B2 for the second view. Blue element B2 is next to a next red element R1 for the first view V1. This pattern R1-G2-B1-R2-G1-B2 is repeated along the direction X.
A horizontal pitch Px of the color elements and a horizontal width Wmx of one metal connection line M2 is indicated in FIG. 1. Note that the configuration of the double stepped barrier is such that the horizontal width of one blocking structure BS plus one opening WO equals two horizontal pitches Px: WO+BS=2*Px, while the horizontal width of one blocking structure BS equals the horizontal width of one opening WO.
The first barrier layer LR1 comprises openings between the blocking structures BS. The locations of these openings of LR1 in the horizontal direction X coincide with blocking structures BS of the second barrier layer LR2. This will be illustrated in FIG. 2 in more detail.
As illustrated by arrows A1, A2, color element B1 contributes to the first view under first viewing angle V1. The color element R2 is adjacent to B1 to the second view under second viewing angle V2 as illustrated by arrows A3, A4. Please note that a gap Gp occurs between the viewing angles V1 and V2 (between arrow A2 and arrow A3). In this manner no cross-talk between the first and second view exists. Note that as illustrated in FIG. 2, the construction of the double barrier is substantially similar in both horizontal and vertical directions. Thus, cross-talk between the first and second view in both the horizontal and vertical directions is absent.
Not shown in this cross-section, for reasons of clarity, is a light-switching layer which comprises light switching elements that are individually associated with a single color element for controlling transmission of light through that single color element.
Light switching elements may be LCD elements which, under control of an electric signal, can set either an opaque state or a transparent state or in one or more intermediate semi-transparent states. Each LCD element typically comprises a layer of liquid crystal material and a thin film transistor (TFT) circuit for controlling the state of the liquid crystal layer. Each light switching element is arranged next to the associated single color element on the color filter plate CF (i.e. in the path of the light passing through the color element).
Each metal connection line M (that extends in a vertical direction Y perpendicular to the plane of drawing) is coupled to a row of TFT circuits. Below this will be explained in further detail.
Also not shown in this cross-section, for reasons of clarity, are first and second polarizing layers. The first polarizing layer is located as a first outer layer between backlight BL and the first lower barrier layer LR1, and the second polarizing layer is located above the second barrier layer LR2 as a second outer layer.
FIGS. 2a, 2b depict a top-view layout of the barrier layers below and above the pixel matrix layer, respectively, as used in the dual view display D1 of FIG. 1. In particular, FIGS. 2a, 2b illustrate the extent of the first and second barrier layers LR1, LR2 in the horizontal direction X and the vertical direction Y. The blocking structures BS of each barrier layer LR1, LR2 are indicated by dark areas while the openings in each of the barrier layers are indicated by the light areas.
As mentioned above, the first and second barrier layers are in ‘anti-phase’: a position of an opening in one barrier layer being covered in the perpendicular direction Z by a blocking structure in the other barrier layer. Also note that besides a difference in vertical and horizontal dimensions, the barrier layers are structured similarly in both directions. The difference in horizontal and vertical dimension relates to the aspect ratio of a sub-pixel: a horizontal width of a sub-pixel is about one third of the vertical width of the sub-pixel. Note that this implies that in the direction Y, the vertical width of an opening plus the vertical width of one blocking structure equals two times a pitch in the vertical direction of one color element including the vertical width of one metal connection line running in the horizontal direction.
As described above, the double barrier dual view display D1 of the prior art requires the use of two barrier layers. This adversely affects the construction of the Dual view display since a variation of the thickness of the glass substrates carrying the barrier layers and the pixel matrix display can affect the quality of a produced image. Moreover, such a double glass layer construction requires two relatively thin glass plates, which results in relatively higher costs for the display. Note also that due to the presence of these two thin glass plates, the variations of thickness of each glass plate must be less than for thickness variations of a single glass plate to obtain a view with similar optical properties in both cases. Also, thinner glass plates are more prone to fracture and damage. For these reasons, dual view displays are preferably constructed by means of a single barrier layer.
FIG. 3 depicts a top view of first stepped barrier. The first stepped barrier SB1 is a single barrier layer capable of providing dual view in the horizontal direction. Blocking structures BS are indicated by dark areas and openings in the barrier layer SB1 are indicated by light areas.
The blocking structures are arranged in rows of a vertical width Wy. In each row, the blocking structures and openings are shifted stepwise in the horizontal direction X over half of a horizontal width Wx. The horizontal width Wx corresponds to two times the horizontal pitch Px as described above.
The vertical width Wy of a row is substantially equal to the vertical width Py (shown in FIG. 4) of a single color element R1, R2 (sub-pixel) including the vertical width of one intermediate metal connection line (or light shield line) running in the horizontal direction. In FIG. 3, the vertical width of the openings WO is substantially equal to the vertical width Wy of a row. Advantageously, this stepwise arrangement of blocking structures may provide an increased (horizontal) resolution of perception by a user in comparison to the vertical line pattern of the straight barrier from the prior art.
The color elements R, G, B in the color filter plate CF are arranged in red, green and blue color stripes adjacent to each other in the horizontal direction X, while each color stripe extends along the vertical direction Y. The dimensions and positions of the color stripes relative to the openings will be described in more detail below.
FIG. 4 depicts a vertical cross-section of a dual view display using the first stepped barrier. The single stepped barrier SB1 is arranged at a distance d below the color filter plate CF, of which a color stripe CS is shown, for example a stripe of red color elements R.
In this arrangement, the color elements alternately contribute to the first view V1 and to the second view V2: color elements R1 of the color stripe contribute to the red component of the first view V1 and the elements R2 contribute to the red component of the second view V2.
A pitch Py in the vertical direction is equal to the vertical width of one color element including one metal connection line M. The vertical width WO of the openings of the single barrier layer SB1 is substantially equal to the vertical width Wy of a row. Thus WO equals Py in this case.
Since, as above, in the vertical direction a width Wbs of a blocking structure BS plus the width WO of one opening equals two times the vertical pitch Py, in this case the vertical width of one opening WO equals the vertical width Wbs of one blocking structure BS.
It can be seen that the first view V1 and second view V2 show an overlap in the vertical direction Y. For one opening in the single barrier layer SB1, the first view V1 has an half viewing angle between arrow A1 and arrow A2, while the second view V2 has a viewing angle between arrow A3 and A4 for the same opening of the barrier layer. An overlapping angle OV occurs between arrow A3 and A2. Thus, this single barrier layer SB1 exhibits a cross-talk OV between first and second views which for practical purposes may not be acceptable. The usable width of view V1 in this configuration is limited by arrow A3 (boundary of second view V2).
FIG. 5 depicts a second stepped barrier SB2 which is a single barrier layer capable of providing dual view in the horizontal direction. Again, blocking structures BS are indicated by dark areas and openings in the barrier layer SB1 are indicated by light areas.
The blocking structures BS are arranged in rows of vertical width Wy. In each row the blocking structures and openings are, in comparison to an adjacent row, shifted stepwise in the horizontal direction X over half of a horizontal width Wx of one blocking structure BS plus one opening.
Like the first stepped barrier SB1, the second stepped barrier SB2 advantageously provides stepwise arrangement of blocking structures that may provide an increased (horizontal) resolution of perception by a user in comparison to the straight barrier as mentioned before. To avoid overlap of the first and second view V1, V2, the vertical width WO of openings in the second stepped barrier SB2 is chosen smaller than the vertical width Py of a color element (sub-pixel).
FIG. 6 depicts a vertical cross-section of a dual view display using the second stepped barrier. The second single stepped barrier SB2 is arranged at a distance d below the color filter plate CF, of which a color stripe CS is shown, for example a stripe of red color elements R.
In this arrangement, the elements R1 of the color stripe contribute to the red component of the first view V1 and the elements R2 contribute to the red component of the second view V2.
The vertical width WO of the openings of the single barrier layer SB2 is smaller than the vertical width Py of a single color element R1, R2.
The increase of the vertical width of the blocking structures with respect to SB1 is indicated by the extensions xb on the blocking structures along line Y.
Since, in the vertical direction the width Wbs of a blocking structure BS plus the width WO of one opening equals two times the vertical pitch Py and WO is chosen smaller than Wy, in this case the vertical width Wbs of one blocking structure BS is larger than the vertical pitch Py (note that Wy equals Py).
It can be seen that the first view V1 and the second view V2 show an overlap OV in the vertical direction Y which is strongly reduced in comparison to the overlap observed for a dual view display that uses the first single stepped barrier SB1. Note that in comparison to the first stepped barrier only, the vertical width WO of the openings and the vertical width of the blocking structures BS have been changed, all other sizes are the same as shown in FIG. 3 and FIG. 4.
Although the second stepped barrier SB2 strongly reduces the overlap OV of the first and second views V1, V2 in comparison to the overlap OV as shown by the dual view display using the first stepped barrier SB1, it is noted that the overlap OV may still be such that the driver may see the second view in a vertical direction above or below the first view. It is, however, possible to design the second stepped barrier SB2 in such a way that substantially no overlap occurs. A practically complete reduction of overlap or cross-talk by reducing the vertical width WO of an opening in the stepped barrier layer SB2 may be possible but at the same time this would strongly reduce the transmitted intensity of the first and second views V1, V2 in an undesirable manner.
The second stepped barrier has an adverse impact on the transmission of light of the dual view display. In comparison to a transmission of first stepped barrier SB1 (normalized at 100%), the second stepped barrier has a transmission of only about 60%. Disadvantageously, such a reduction of transmission would require a light source with higher intensity and a higher power consumption.
Disadvantageously, such a reduction of transmission would require a light source with higher intensity and a higher power consumption.